1. Field of the Invention
The present invention generally relates to a planar light-emitting device. More specifically, the present invention relates to a planar light-emitting device in which a point light-emitting element such as an LED (Light Emitting Diode) is used as a light source element.
2. Background Information
FIG. 5 is a top plan view of a conventional planar light-emitting device. FIG. 6 is a diagram illustrating light emission characteristics of the planar light-emitting device illustrated FIG. 5.
With the conventional planar light-emitting device in FIG. 5, an LED 130 is housed as a point light-emitting element in the center of a circular hole 120 formed in a light guide plate 110. The hole 120 is located near the flat, side end face of the light guide plate 110. The above-mentioned side end face is formed as a reflecting face 111 by applying a reflective sheet, reflective tape, or another such optically reflective film 140 to this side end face. In FIG. 5, 150 is an LED substrate on which the LED 130 is mounted.
With the conventional planar light-emitting device, light that comes out of the LED 130 moves out through the area around the LED 130, passes through the walls of the hole 120, and goes into the light guide plate 110. Light that has entered the light guide plate 110 moves out in all directions around the hole 120 as indicated by the arrows in FIG. 5, and comes out of a light emitting face formed by one face of the light guide plate 110, so that the light guide plate 110 emits planar light. Also, part of the light that has come out of the LED 130, passed through the walls of the hole 120, and entered the light guide plate 110 becomes return light upon being reflected by the reflecting face 111, which is formed by the flat, side end face of the light guide plate 110.
Meanwhile, another conventional backlight is also known (see Japanese Laid-Open Patent Application Publication No. 2006-19141, for example). This backlight is such that a side face emitting type of LED disposed on an LED array substrate is disposed in a recess of a light guide plate. A diffusive and reflective sheet is disposed on the lower face of the light guide plate, a diffusive sheet on the upper face of the light guide plate, and a reflective sheet on the side end face of the light guide plate.
Furthermore, another conventional backlight is also known (see Japanese Laid-Open Patent Application Publication No. 2006-351522, for example). With this backlight, two light guide plates are disposed on both sides of an LED. Reflective sheets are disposed on the lower faces of the light guide plates, and an isolation sheet is disposed on the upper faces of the light guide plates. A peaked reflector is disposed on the isolation sheet. A diffusing sheet is disposed above and a specific distance away from the isolation sheet, and an optical sheet is disposed over this diffusing sheet, forming a hollow portion between the diffusing sheet and the isolation sheet. A semi-cylindrical reflector is provided to the side of the light guide plates, and light that comes out of the side end faces of the light guide plates is guided by the reflector to the hollow portion, reflected by the surface of the peaked reflector, and is emitted through the diffusing sheet and the hollow portion to the outside.
As yet another known example of prior art, there has been research into a backlight device in which light utilization efficiency is improved by disposing a highly reflective member (one with high optical reflectivity) near an LED light source, so that the brightness of the liquid crystal panel is improved (see Japanese Laid-Open Patent Application Publication No. 2004-31064, for example).